1. Field of the Invention
The present invention relates to a stereoscopic image display technique. More specifically, the present invention relates to a stereoscopic image display device and the like for converting an image to a stereoscopic image with which an observer does not feel a sense of discomfort even when the observer changes one's position.
2. Description of the Related Art
Recently, television sets capable of viewing stereoscopic images are on the general market. Accordingly, the amount of the stereoscopic image contents is increased, and the environments for viewing the stereoscopic images are coming to be in good condition. In general, the observer wears eyeglasses for stereoscopic image display to project images of different parallaxes on left and right eyes so that the observer can view the stereoscopic image on the stereoscopic image television set. However, there are many observers who feel a sense of displeasure to wear the eyeglasses for stereoscopic image display, and a stereoscopic image display device that requires no such eyeglasses is desired. Further, when the eyeglass-type stereoscopic image display device is utilized as a mobile device, it is inconvenient since the stereoscopic image display device and the eyeglasses for stereoscopic image display are required to be carried to the outside. Thus, such stereoscopic image display device that requires no eyeglasses is more strongly desired for mobile use.
As the stereoscopic image display that requires no eyeglasses for stereoscopic image display, generally used is a type which divides spatial areas for projecting a stereoscopic image, and projects images of different parallaxes to each of the divided spatial areas so as to project images of different parallaxes to the left and right eyes of the observer. Through providing a lenticular lens and a parallax barrier on a stereoscopic display panel of the stereoscopic display device, the images of different parallaxes are provided for each of the divided spatial areas.
With such-type of stereoscopic image display device, it is not necessary to wear the eyeglasses for stereoscopic image display. Thus, it is excellent in terms of avoiding such trouble of wearing eyeglasses and is expected to be utilized in mobile use in particular. However, images of different parallaxes are projected by being spatially isolated with such type, so that the spatial area where the observer can visually recognize the stereoscopic images properly becomes limited. The spatial area where the observer can visually recognize the stereoscopic images properly is limited to a case where the position of the left eye of the observer is within the spatial area where the left-eye image is projected and the position of the right eye of the observer is within the spatial area where the right-eye image is projected. When the positions of the left and right eyes of the observer are shifted from those spatial areas, the left-eye image and the right-eye images overlap on one another. This results in projecting a video of 3D-crosstalk images (CT-images) to the observer.
Now, the spatial areas divided by the stereoscopic display panel will be described by referring to the accompanying drawings. First, described is the spatial area in a case where a parallax barrier is used for the stereoscopic display panel. FIG. 84 shows an example of an optical model in which images of different parallaxes are projected to the left and right eyes of an observer with the parallax-barrier type stereoscopic image display device. FIG. 84 is a sectional view observed from the above the head of the observer, in which the both eyes (right eye 55R and left eye 55L) of the observer are located on an observing plane 30 at a distance of an optimum observing distance OD from the display plane of the display device, and the center of the both eyes of the observer and the center of the display panel match with each other.
The image display panel (not shown) is constituted with a group of optical modulators that are pixels arranged in matrix (e.g., a liquid crystal panel). In FIG. 84, among the right-eye pixels 4R and the left-eye pixels 4L arranged alternately, only each of the pixels at both ends of the image display panel and in the center are illustrated. A parallax barrier 6 that functions as a means for dividing a spatial area and projecting images is disposed on the far side of the display panel from the observer. The parallax barrier 6 is a barrier (a light shielding plate) on which a great number of thin vertical striped slits 6a are formed, and it is disposed in such a manner that the longitudinal direction of the barrier itself becomes orthogonal to the direction along which the left-eye pixels 4L and the right-eye pixels 4R of the image display panel are arranged. In a still far side of the parallax barrier, a light source (not shown: so-called backlight) is placed. Light emitted from the light source transmits through the slits 6a and is projected towards the observer while the intensity thereof is being modulated in the pixels within the image display panel. The projecting directions of the right-eye pixel 4R and the left-eye pixel 4L are limited by the existence of the slits 6a. 
When a locus of the light passing through the closest pixel among the light emitted from each of the slits 6a is illustrated as a light ray 20, a right-eye area 70R (a spatial area where the right-eye image is projected) where the projection images of all the right-eye pixels 4R are superimposed and a left-eye area 70L (a spatial area where the left-eye image is projected) where the projection images of all the left-eye pixels 4L are superimposed can be acquired. Only the projection images from the right-eye pixels 4R can be observed in the right-eye area 70R, and only the projection images from the left-eye pixels 4L can be observed in the left-eye area 70L. Therefore, when the parallax images are projected to the left and right eyes while the right eye 55R of the observer is located within the right-eye area 70R and the left eye 55L is located within the left-eye area 70L, the observer visually recognizes those as a stereoscopic image. In other words, the observer can observe a desired stereoscopic image when the right eye 55R is located within the right-eye area 70R and the left eye 55L is located within the left-eye area 70L. The display device shown in FIG. 84 is so designed that the projection images (width P′) at the optimum observing distance OD of each of the right-eye pixel 4R and the left-eye pixel 4L (width P) all superimposed with each other so that the width of the right-eye area 70R and the left-eye area 70L becomes the maximum on an observing plane 30. The width P′ of the projection image is mainly determined based on the distance h between the slit 6a and the pixel, the pixel pitch P, and the optimum observing distance OD. When the width P′ is widened, the width of the right-eye pixel 70L and the left-eye pixel 70L is widened. However, it is impossible to locate each of the both eyes of the observer at arbitrary positions, so that the stereoscopic area where the stereoscopic images can be sighted cannot necessarily be expanded. Provided that the distance between both eyes is e, it is preferable to design the width P′ to be equivalent to the space e between the both eyes. In a case where the width P′ is smaller than the space e between the both eyes, the area of stereopsis is limited to the width P′. In the meantime, in a case where the width P′ is larger than the space e between the both eyes, the area where the both eyes are located in the right-eye area 70R or the left-eye area 70L is simply increased. Note that a far observing distance FD, a near observing distance ND, and a slit width S are written in FIG. 84.
Further, FIG. 85 shows an optical model of a case where the parallax barrier 6 is disposed on the front side of the display panel when viewed from the observer. As in the case where the barrier is disposed on the far side of the display panel when viewed from the observer, the observer is at the optimum observing distance OD, and the projection images (width P′) of each of the left-eye and right-eye pixels (width P) are designed to superimpose with each other on the observing plane 30. When a locus of the light passing through the closest slit 6a among the light emitted from each of the pixels is illustrated as the light ray 20, the right-eye area 70R where the projection images of all the right-eye pixels 4R are superimposed and the left-eye area 70L where the projection images of all the left-eye pixels 4L are superimposed can be acquired.
Next, FIG. 86 shows spatial areas divided when a lenticular lens is used instead of the parallax barrier. In FIG. 86, only the parallax barrier 6 of FIG. 85 is changed to the lenticular lens 3. Note that a cylindrical lens width L is written in FIG. 86.
Next, a case where the observer is located in a 3D-crosstalk viewing space away from an area (stereoscopic viewing space) where the observer can visually recognize a stereoscopic image properly will be studied by using the lenticular-lens type optical model. FIG. 87 is a sectional view when observed from above the head of the observer when the observer moves to the right side so that the right eye 55R comes to be located at the boundary between the right-eye area 70R and the left-eye area 72L and the left eye 55L comes to be located at the boundary between the right-eye area 70R and the left-eye area 70L.
In this case, the light ray 20 passing through the principal point (vertex) of the closest cylindrical lens 3a among the light emitted from the right-eye pixels 4R and a light ray 21 passing through the principal point (vertex) of the second closest cylindrical lens 3b among the light emitted from the left-eye pixels 4L are both projected to the position of the right eye 55R of the observer. That is, in FIG. 87, the observer observes the projection images from both the right-eye pixels 4R and the left-eye pixels 4L with the right eye 55R. Thus, when a stereoscopic image is observed, the right-eye pixels 4R and the left-eye pixels 4L are superimposed to produce a double image (so-called 3D-crosstalk image (CT-image)). Therefore, a desired stereoscopic image cannot be sighted. Note here that the area of the boundary between the right-eye area 70R and the left-eye area 72L and the area of the boundary between the right-eye area 70R and the left-eye area 70L are the 3D-crosstalk viewing spaces.
As described above, with the stereoscopic image display device that requires no eyeglasses for stereoscopic image display, an issue of having a CT-image caused by 3D crosstalk occurs depending on the observing position of the observer. Therefore, the observer feels a sense of discomfort, which is a reason for preventing the stereoscopic image display devices from being spread.
In order to overcome the above-described issue, there is proposed a method which lightens the influence of 3D crosstalk by adding black-side correction data or white-side correction data to the image area where the luminance value within the left-eye image (L image) and the right-eye image (R image) of a stereoscopic image content are changed by 3D crosstalk generated by retardation of the liquid crystal of a time-division type stereoscopic image display device. Further, there is also proposed a method which lightens the influence of CT-images caused by 3D crosstalk through adding smooth correction data by applying image blurring processing such as lowpass filter and the like on the black-side correction data and the white-side correction data so that the CT-image becomes hard to be recognized by human eyes (Japanese Unexamined Patent Publication 2011-166744 (Patent Document 1)).
Further, also proposed are methods which lighten the influence of CT-images caused by 3D crosstalk through generating image data from which image components mixed by 3D crosstalk is subtracted and displaying the acquired data (Japanese Unexamined Patent Publication 2001-298754 (Patent Document 2), Japanese Unexamined Patent Publication 2002-095010 (Patent Document 3)). When α % of image components of the R image are mixed into the L image by 3D crosstalk, correction processing of the image data is performed by using a following formula (1).Lf(x,y)=Lc(x,y)−α×Rc(x,y)  Formula (1)Note here that Lf(x, y) shows the luminance value of the L image after performing the correction processing, while Lc(x, y) shows the luminance value of the L image of the stereoscopic image content as the original data. Further, α shows the 3D crosstalk amount (proportion of the image components to be mixed), and Rc(x, y) shows the luminance value of the R image of the stereoscopic image content as the original data, respectively.
Further, also proposed is a method which lightens the influence of CT-images caused by 3D crosstalk through converting one of two-viewpoint image data into a black image and projecting only the other image data at the observing position where a CT-image generated by 3D crosstalk is projected (Japanese Unexamined Patent Publication 2008-089787 (Patent Document 4)).
Furthermore, also proposed is a stereoscopic image display device which lightens the influence of CT-images caused by 3D crosstalk through measuring the observing position of the observer and performing luminance adjustment processing within sub-pixels which generate multiple-viewpoint parallax images depending on the observing positions (Juyong Park, et al, “Active Crosstalk Reduction on Multi-View Displays Using Eye Detection” SID2011, 61. 4, pp. 920-923 (Non-Patent Document 1)).
Moreover, also proposed is a method which lightens the influence of CT-images caused by 3D crosstalk generated by delay at the time of switching the shutter of the eyeglasses through applying image blurring processing such as lowpass filter and the like on the left-eye image (L image) and the right-eye image (R image) of the stereoscopic image based on the parallax amount with a liquid crystal shutter eyeglass type stereoscopic image display device (Japanese Unexamined Patent Publication 2011-040946 (Patent Document 5)).
Further, also proposed is a method which shortens the time for displaying a CT-image caused by 3D crosstalk through expanding the dynamic range of the luminance value of the image data for lightening the influence of the CT-image by 3D crosstalk generated due to shift (change in the speed) in the timing of the eyeglass shutter, the timing of the liquid crystal panel, and the timing of the backlight with a liquid crystal shutter eyeglass type stereoscopic image display device (Yuki Iwanaka, et al, “Image Processing-based Crosstalk Reduction for Stereoscopic Displays with Shutter Glasses” SID2011, 55. 4, pp. 816-819 (Non-Patent Document 2)).
Furthermore, also disclosed is a method which lightens the influence of the CT-image caused by 3D crosstalk even in a case where stereoscopic image display devices of various display types are used through switching the image to the image data that lightens the influence of the CT-image caused by 3D crosstalk in accordance with the display types (liquid crystal shutter eyeglass type, polarization eyeglass type) of the stereoscopic image display device (Japanese Unexamined Patent Publication 2012-039592 (Patent Document 6)).
Further, even when stereoscopic image contents of same parallax are displayed, the parallax of the stereoscopic image contents observed by the observer changes depending on the distance between the stereoscopic image display device and the observing position of the observer. There is also proposed a method which displays a stereoscopic image by adjusting the parallax of the stereoscopic image content according to the distance between the stereoscopic image display device and the observing position of the observer in order to overcome such an issue that the stereoscopic image cannot be sighted when the distance between the stereoscopic image display device and the observing position of the observer becomes too small so that the parallax of the stereoscopic image contents becomes too large (Japanese Unexamined Patent Publication 2012-044308 (Patent Document 7)).
Furthermore, the stereoscopic image display device gives a sense of discomfort called an image frame distortion to the observer when the popup-displayed stereoscopic image content is hidden in the image frame and displayed partially. In a case of a flat image display, the image content is in a rear position with respect to the image frame, so that the observer visually recognizes that the whole scene of the content is not shown. However, in a case of a stereoscopic image display, the observer feels a sense of discomfort since the stereoscopic image content is displayed with a part thereof being hidden by the image frame even when the stereoscopic image is displayed on the front side with respect to the image frame. Thus, there is proposed a method which makes the stereoscopic image content displayed on the outside of the stereoscopic display area that is the cause for the image frame distortion transparent so that it is not displayed, in order to overcome the issue of the image frame distortion in the multi-viewpoint type stereoscopic image display device (Japanese Unexamined Patent Publication 2005-252459 (Patent Document 8)).
Further, also proposed is a method which performs blurring processing on the image data to be the stereoscopic image in order to lighten fatigue caused by viewing the stereoscopic image (Japanese Unexamined Patent Publication 2011-082829 (Patent Document 9)).
Furthermore, an object at a far distance is viewed in an out-of-focus state with human eyes due to the focus function of the human eyes. However, in a case of displaying a stereoscopic image on the stereoscopic image display device, the out-of-focus state caused due to the focus function of the human eyes does not occur since the stereoscopic image is projected from the panel on the same plane. In order to lighten such state, there is proposed a method which measures the observing position of the observer and performs blurring processing of the image data to be the stereoscopic image (Japanese Unexamined Patent Publication 2011-244349 (Patent Document 10)).
With the naked-eye stereoscopic image display device that requires no eyeglasses for stereoscopic image display, there is a large influence of a CT-image caused by 3D crosstalk depending on the observing position of the observer. This gives not only a sense of discomfort to the observer but also is one of the factors for causing physiological instability such as feeling video sickness and eye fatigue in a case of a stereoscopic image display device with a low picture quality, which is a reason for preventing the naked-eye stereoscopic image display device from being spread.
As a method for overcoming such issue, Patent Document 1 is proposed. However, the method of Patent Document 1 does not adjust the blurring amount of the image data by taking the observing position of the observer in to consideration. Therefore, it is not possible to perform the image blurring processing for lightening the influence of the CT-image caused by 3D crosstalk when the observing position of the observer is shifted.
Further, the methods of Patent Documents 2 and 3 lighten the influence of the CT-image caused by 3D crosstalk by subtracting the image components mixed by 3D crosstalk from the image data. However, the image processing method executed by subtraction can only be applied when the 3D crosstalk amount is small and the amount of the image component to be mixed is small. When the 3D crosstalk amount is large, the image component to be mixed cannot be subtracted from the original image data. Thus, there appears an image area from which the mixed image component cannot be removed completely. Therefore, when the observing position of the observer is shifted and the 3D crosstalk amount is increased, the influence of the CT-image caused by 3D crosstalk cannot be lightened.
Further, with the method of Patent Document 4, it is possible to remove the influence of the CT-image caused by 3D crosstalk through converting one of the image data to a black image. However, only the other image data is projected towards the observer, so that the luminance value of the image data projected towards the observer is deteriorated. Furthermore, while increasing the output of the backlight as a countermeasure for the deterioration of the luminance value is depicted in Patent Document 4, it causes increase of the power consumption, shortening of the life of the backlight, and the like. Moreover, with the stereoscopic image display device which projects the two-viewpoint image data (right-eye image and left-eye image) towards the observer, there is a possibility of projecting only the black image to one of the eyes of the observer when one of the image data is converted into the black image. Therefore, the image processing method of Patent Document 4 cannot be applied.
With Non-Patent Document 1, it is possible to lighten the influence of CT-images caused by 3D crosstalk through measuring the observing position of the observer and performing luminance adjustment processing on the sub-pixels which generate multiple-viewpoint parallax images depending on the observing positions. However, the luminance adjustment processing on the order of sub-pixel is required, so that the processing becomes complicated. Further, as in the case of Patent Document 4, with the stereoscopic image display device which projects the two-viewpoint image data (right-eye image and left-eye image) towards the observer, there is a possibility of projecting only the sub-pixels whose luminance value is deteriorated to one of the eyes of the observer when the luminance value is deteriorated by the luminance adjustment processing performed on the sub-pixels. Therefore, the image processing method of Non-Patent Document 1 cannot be applied.
Further, with Patent Document 5 and Non-Patent Document 2, it is possible to lighten the influence of CT-images caused by 3D crosstalk in the liquid crystal shutter eyeglass type stereoscopic image display device. However, there is no consideration regarding a countermeasure for 3D crosstalk generated in the naked-eye type stereoscopic image display device, and the blurring amount of the image data is not adjusted by considering the observing position of the observer. Thus, when the observing position of the observer is shifted, the image blurring processing for lightening the influence of the CT-image caused by 3D crosstalk cannot be performed.
Further, Patent Document 6 discloses the method which displays the image by switching it to the image data that lightens the influence of 3D crosstalk in accordance with the display type of the stereoscopic image display device. However, it does not consider the display type of the naked-eye type stereoscopic image display device, so that it is not possible to lighten the influence of 3D crosstalk with the naked-eye type stereoscopic image display device.
Furthermore, Patent Document 7 discloses the method which performs parallax adjustment processing on the stereoscopic image content in accordance with the distance between the stereoscopic image display device and the observing position of the observer. However, it does not consider any image filtering processing method (parallax adjusting amount calculation method) for lightening the influence of the CT-image caused by 3D crosstalk appearing in the naked-eye type stereoscopic image display device which projects the image by spatially separating it into the right-eye image and the left-eye image by using a lenticular lens or a parallax barrier, so that the influence of the CT-image caused by 3D crosstalk cannot be lightened.
Further, Patent Document 8 proposes the method which makes the stereoscopic image contents displayed on the outside of the stereoscopic display area that is the cause for the image frame distortion transparent so that it is not displayed. However, it does not consider any image filtering processing method (method which makes the image transparent so as not be displayed) for lightening the influence of the CT-image caused by 3D crosstalk appearing in the naked-eye type stereoscopic image display device which projects the image by spatially separating it into the right-eye image and the left-eye image by using a lenticular lens or a parallax barrier. Thus, the influence of the CT-image caused by 3D crosstalk cannot be lightened.
Further, Patent Document 9 proposes the method which performs blurring processing on the image data to be the stereoscopic image. However, it does not consider any image filtering processing method (image blurring) for lightening the influence of the CT-image caused by 3D crosstalk appearing in the naked-eye type stereoscopic image display device which projects the image by spatially separating it into the right-eye image and the left-eye image by using a lenticular lens or a parallax barrier, so that the influence of the CT-image caused by 3D crosstalk cannot be lightened.
Further, Patent Document 10 proposes the method which measures the observing position of the observer and performs blurring processing of the image data to be the stereoscopic image. However, it does not consider any image filtering processing method (image blurring) for lightening the influence of the CT-image caused by 3D crosstalk appearing in the naked-eye type stereoscopic image display device which projects the image by spatially separating it into the right-eye image and the left-eye image by using a lenticular lens or a parallax barrier, so that the influence of the CT-image caused by 3D crosstalk cannot be lightened.
It is therefore an exemplary object of the present invention to overcome the above-described issues and to provide a stereoscopic image display device and the like with which the influence of the CT-image caused by 3D crosstalk is lightened so that the observer does not feel a sense of discomfort even when the observing position of the observer is shifted even with the naked-eye type stereoscopic image display device.